Lymphoid Tissues Flashcards
What are the 2 parts of the lymphatic system?
- Lymphatic vessels
- Lymphoid tissue
What are the 3 types of lymphoid tissue?
- Primary
- Secondary
- Tertiary
What are the 7 main lymph nodes?
- Cervical
- Axillary (armpit)
- Mesenteric (abdomen)
- Para-aortic
- Inguinal (leg meets body)
- Popliteal (behind knee)
- Superficial and deep (all around)
What are primary lymphoid organs?
Where lymphopoiesis occurs
What are the 3 primary lymphoid organs?
- Fetal liver
- Bone marrow
- Thymus
Which 2 cells are comprise the adaptive immune response?
- T lymphocytes
- B lymphocytes
What is the adaptive immune system?
2nd line immune defence
What are the 2 hallmarks of the adaptive immune response?
- Specificity
- Memory
How are lymphoid organs structured to facilitate adaptive immunity?
- All around the body
- Keep B and T lymphocytes separated
What is the immunological repertoire?
The range of distinct T or B lymphocytes in a host
What are the 2 sites of haematopoiesis in a foetus?
- All bones
- Liver/spleen
Which 4 bones does haematopoiesis occur in in adults?
- Vertebrae
- Iliac bones (in pelvis)
- Ribs
- End of long limb bones (eg. femur)
What can be seen in the cross-section of bone marrow? (2)
- Inner yellow marrow —> fat
- Outer red marrow —> lymphopoiesis
Where is the thymus?
Sits on heart
What are the 3 steps of stepwise differentiation of T cells in the thymus?
- Positive selection
- Negative selection
- Final selection and exit
What is positive vs negative T cell selection?
- Positive —> check TCRs (receptors) are expressed
- check if can recognise antigens - Negative —> check T cells don’t react to self-antigens
- prevent autoimmune disease
Where does positive and negative T cell selection occur?
Thymus
What happens to the thymus over time?
Thymic involution
What is thymic involution?
Thymus shrinks with age
(Adipose tissue replaces functional thymic tissue)
What is the TCR?
T cell repertoire
How many different T cells do genes allow for?
10^15-10^20
What are secondary lymphoid organs?
Where lymphocytes can interact with antigens and other lymphocytes
Why is the lymphatic system needed?
Need to specific lymphocyte to pathogen which may lie anywhere in the body
What are 6 secondary lymphoid organs?
- Tonsils
- Spleen
- Lymph nodes
- Apendix
- Mucosal-associated lymphoid tissue (MALT)
How are different lymphoid tissues interconnected? (2)
- Lymphatic system (lymph in vessels)
- Blood
Are lymphoid tissues always whole organs?
No-may just be part of the organ
What are afferent and efferent lymphatic vessels mean?
- Afferent —> takes lymph into node
- Efferent —> takes lymph out of node
What happens at an activated germinal centre?
B cells undergo mutation and selection to generate high affinity antibodies
What are the 7 parts of a lymph node?
- Afferent and efferent lymphatic vessels
- Artery and vein
- Medullary sinus (innermost)
- T cell area
- Germinal centre
- Lymphoid follicle (mostly B cells)
- Marginal sinus (outermost)
Where is lymph in the spleen?
Inner white pulp
(Surrounded by outer red pulp)
What is the first line of defence against infection?
Epithelial barriers
Where do lymph nodes cluster? (3)
- Near mucosal tissue (GI/U/R tracts etc.)
- End of long limbs
What are Peyer’s patches?
Type of MALT
Where are Peyer’s patches found?
Below epithelium of ileum
Why are Peyer’s patches present under the ileum’s epthelium? (2)
- Lots of entry of pathogens from food
- Maintain microbiome balance
What do follicles contain many of?
Germinal centres —> B cells
What is the arrangement of Peyer’s patches and follicles?
Follicles lie under Peyer’s patches
What are the 4 types of tonsils?
- Pharyngeal (pharynx between nose and mouth)
- Tubular (opening of auditory tubes)
- Palantine (back of throat)
- Lingual (base of tongue)
Where do tonsils encircle?
Oral and nasal cavity
How are tonsils activated?
Oral antigens
What is the Waldeyer ring?
Ring of lymphoid tissue in the pharynx
- contains all 4 types of tonsils
What do tonsils contain many of? (2)
- Germinal centres
- Lymphoid follicles
How do lymphocytes and antigens reach secondary lymphoid organs?
Drained into lymph —> travels through lymphatic vessels
Where are secondary lymphoid organs distributed?
All around the body
How much lymph is returned to the blood each day?
2-3L
How frequently does each naive T cell recirculate?
Every 24 hours
What is retained at sites of inflammation?
B and T cells
How are naive T cells moved into lymph nodes? (
Extravasation through high endothelial venules (HEVs)
1. Chemotaxis
2. Adhesion
3. Rolling
4. Activation
5. Arrest
6. Diapedesis
Which 2 naive T cell proteins bind to HEVs for extravasation?
- Selectin (L-selectin to CD34)
- Integrin (LFA-1 to ICAM-1)
Where does naive cell extravasation occur?
High endothelial venules
Why do wounds lead to inflammation?
Drain lots of fluid to site —> dentritic cells and lymphocytes reach area
What is antigen presentation?
Display of antigens to T cell via MHC I or II (major histocompatibility complexes)
Which cells immediately respond to wounding and why?
Dendritic cells
Where do dendritic cells migrate to when skin is infected and why?
Lymph nodes via afferent lymph
- Present antigen to T cells
What are langerhans cells?
Dendritic cells in the skin that detect the presence of pathogens or antigens at the site of infection
What are intraepidermal lymphocytes?
Lymphocytes in skin epidermis
How are antigens presented by denritic cells? (4)
- Phagocytosis or intracellular viral protein production gets antigen inside DC
- Antigens degraded to small protein fragments
- ER converts fragments to MHC-I
- MHC-I presented on DC surface membrane
Where do antigens and their specific T cell usually meet?
Lymph nodes
When do we generate most of our naive T cells?
Childhood
What happens to naive T cells that do not show proper positive or negative selection?
Apoptosis
